The preferred embodiment concerns a method and a device to detect an electrical potential and electrical charges, in which a capacitive sensor that has a first electrode or at least one second electrode situated opposite the first electrode is used as a measurement arrangement. A toner or charge image is generated on the generated surface of an endless intermediate image carrier. A drive unit drives the intermediate image carrier so that the generated surface is directed in a revolving manner past the first electrode situated opposite the generated surface. The first electrode is electrically connected with an evaluation unit that evaluates the measurement signals of the measurement arrangement. The second electrode can in particular be formed by a low-resistance, electrically conductive layer of the intermediate image carrier that is advantageously connected with a reference potential of the printer or copier.
Known devices in electrographic printers or copiers that use a capacitive sensor as a measurement arrangement are in particular used to detect the layer thickness of a toner particle layer and the moisture content of a carrier material. Such a device and an associated measurement method are known from the document DE 101 51703 A1.
A device and a method to continuously control the bias voltage of an electrographic developer unit are known from the document U.S. Pat. No. 3,918,395, in which a measurement arrangement is used that has an electrically conductive plate situated opposite the generated surface of a photoconductor. A voltage that is used to set the bias voltage is induced upon passage of the electrostatic image.
Potential sensors to determine the charge of a photoconductor that have an electrode situated opposite the generated surface of the photoconductor are known from the document WO 91/18287 and from the document DE P 43 36 690 C2.
The content of the cited documents is herewith incorporated by reference into the present Specification.
Additional measurement arrangements for the examination of a toner mark are known from the documents U.S. Pat. No. 5,689,763, DE-A-10151703, JP-A-06130768, DE-A-4336690, JP-A-2006072072 and JP-A-06074985. At least three potential sensors that respectively determine the potential of a toner layer are provided for this in the document JP-A-06130768. From the document U.S. Pat. No. 5,689,763 it is known to determine both the potential and the layer thickness of a colorant layer in a single measurement procedure. The evaluation of the measurement signal determined in the measurement procedure is thereby relatively complicated.
In the prior art known from the document DE-A-4336690, a potential measurement is conducted with the aid of a single sensor. The sensor has a knife-shaped electrode. This electrode is arranged perpendicular to a surface inked with toner particles.
In the prior art known from the document JP-A-2006072072, a measurement arrangement with multiple sensors is used. A first sensor is provided to determine the toner density, and a second sensor is provided to determine the potential of the toner particle layer.
In the prior art known from the document JP-A-06074985, the potential of a toner particle layer is determined with the aid of a first measurement determination. A laser distance measurement to determine the layer thickness of the toner particle layer is conducted via an additional, independent measurement device.